Silica-enriched eucalyptus wood with improved moisture resistance, decay resistance and fire response

Fast-growing eucalyptus is susceptible to moisture-induced dimensional changes and fungal decay. This study evaluated the moisture resistance, decay resistance and qualitative fire response of Eucalyptus urophylla × E. grandis treated with a combined 3-aminopropyltriethoxysilane (APTES)/tetraethyl orthosilicate (TEOS) formulation. Vacuum-pressure impregnation produced APTES/TEOS-treated eucalyptus composites (SEC) with a weight percent gain of 31.56%. Scanning electron microscopy with energy-dispersive X-ray spectroscopy showed Si- and O-rich deposits in cell lumens and cell-wall regions. Relative to the untreated control, the volumetric swelling coefficient decreased from 15.3% to 5.4%, and 24 h water absorption decreased from 105.90% to 69.24%. Mass losses after 12 weeks of exposure to Trametes versicolor and Poria vaporaria were 8.90% and 3.63%, respectively, corresponding to Class I under the ASTM D2017 mass-loss classification adopted in this study. In a qualitative open-flame test, residual mass was 70.31%, and self-extinguishing time was 110 s shorter than that of the control. Fourier transform infrared (FTIR) spectra showed overlapping wood and siloxane-region bands, consistent with silica-rich deposition. Overall, the treatment produced silica-enriched eucalyptus wood with lower water uptake, swelling and fungal mass loss, together with greater residual mass and faster self-extinguishment in the laboratory open-flame test.